Near-term Task Force Recommendation 2.1 Seismic

Hazard Evaluation

Pacific Gas & Electric CompanyPublic MeetingApril 28, 2015

References and Logistics

• Public Meeting Agenda – ML15105A528• NRC Presentation Slides – ML15117A226• Licensee Presentation Slides – ML15117A069• Licensee Hazard Report – ML15070A607 and

ML15070A608• Meeting Feedback Form (request from

njd2@nrc.gov) • Webcast Archive at http://video.nrc.gov• Meeting Summary to be issued within 30-day

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Meeting Purposes

• Gather additional information based on early identification of areas where additional technical information will support the staff’s review

• Gain a better understanding of how the licensee conducted their evaluation

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Outline

• Background of NRC Near-term Task Force Recommendation 2.1 (NTTF R2.1)

• Current NRC approach to seismic hazard characterization

• Hazard characterization for NTTF R2.1• Potential outcomes • Focus questions for NRC review• Timeline

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NTTF Report and Recommendations

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NRC 50.54(f) activities to address NTTF Seismic Recommendations

50.54(f) Request for Information Letter issued March 12, 2012 • Enclosure 1 (or R2.1):

Seismic hazard and risk reevaluation

• Enclosure 3 (or R2.3): Seismic Walkdowns

• Other enclosures addressed flooding and emergency response

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NTTF 2.3 – Seismic Walkdowns – COMPLETED reviews June 2014 Licensees identify and address degraded, nonconforming, or unanalyzed conditions relative to a plant’s current licensing and design bases.

NTTF 2.1 – Interim Expedited Approach (ESEP) CEUS: 12/31/2014; WUS: 1/16If the design basis does not bound reevaluated hazard: Licensees perform interim evaluation to demonstrate key pieces of equipment for core cooling at a higher hazard using installed FLEX equipment up to 2 x SSE.  Evaluate need for modifications while longer‐term risk evaluation is performed.

NTTF 2.1 – Hazard Reevaluations: SUBMITTED CEUS:3/2014; WUS:3/2015Licensees reevaluate hazard based on present day guidance/methods used to define the design basis for new reactors. 

Regulatory Actions NRC staff determines whether additional regulatory actions are necessary to provide additional protection against the updated hazards.

NTTF 2.1 – Interim Evaluation: COMPLETED CEUS: 4/2014; WUS: 4/2015If the design basis does not bound reevaluated hazard: Licensees evaluated the need for interim evaluations using new seismic sources and ground motion with old hazard while the longer‐term risk evaluation is performed.

NTTF 2.1 – Seismic Risk Evaluations: June 2017 – 2020If the design basis does not bound reevaluated hazard: Licensees determine perform a seismic risk evaluation.

Tiered-approach to Seismic Activities

Probabilistic Approach

• Previous studies such as 2011 Shoreline Fault Report and 2014 Coastal Commission Report were deterministic– Few selected scenario earthquakes– Limited treatment of uncertainty

• NTTF Recommendation 2.1 calls for seismic hazard reevaluations at each nuclear power plant using current NRC regulations

• Current NRC regulations and guidance specify a probabilistic approach for developing design ground motions

• Probabilistic ground motion hazards are characterized by a Ground Motion Response Spectrum or GMRS

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Development of Seismic Hazard for R2.1 Reevaluations

• Licensees perform probabilistic seismic hazard analyses following NRC guidance (Regulatory Guide 1.208)

• CEUS licensees (96 units/59 sites)– Previously approved SSHAC Level 3 Models– Plant‐specific site analyses

• WUS licensees (6 units/3 sites)– Regional source and ground motion models developed by each 

Licensee using SSHAC Level 3 Studies– Plant‐specific site analyses

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Screening Approach for R2.1 Reevaluations

• Screening approach specified in Industry Screening, Prioritization, and Implementation Details (SPID) Guidance

• SPID provides detailed guidance for– Development of GMRS– Seismic Risk Evaluations & Limited Scope Evaluations

(high frequency, SFP)• Plants with GMRS > SSE “Screen In” for

– Interim Evaluations (and actions, as needed)– Expedited Interim Evaluations (and actions, as

needed)– Seismic Risk Evaluations

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Potential Outcomes for R2.1 Reevaluations

No Further Analysis

Industry Testing Program for High FrequencySensitive components

Outcome 1

Outcome 2

Outcome 3

NRC Review of SSHAC Studies for WUS Sites

• Did SSHAC process follow NRC guidance?• How effective was the peer review panel?• Have all applicable data been considered?• Were data uncertainties identified and

considered?• Was an appropriate range of applicable models

considered?• How were models selected and weighted in the

analysis?• How were models assembled into the PSHA?

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NRC Review of Source Models for WUS Sites

• How were seismic sources identified? – Geologic mapping– Geophysical observations– Earthquake catalog

• How were seismic sources characterized?– Geometry (location, length, dip)– Range of magnitudes– Faulting style (normal, reverse, strike-slip)– Slip rate and recurrence models– Complex rupture scenarios

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NRC Review of Ground Motion Models and Site Response for WUS Sites

• Do final ground motion models capture a reasonable range of alternative models?

• How were sources of uncertainty captured in model development?

• How were ground motion models adjusted for local site geology?

• Does site response analysis cover a reasonable range of alternative soil/rock properties?

• How was uncertainty in site response analysis incorporated into final probabilistic hazard curves?

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2012 2013 2014 2015 2016 2017 2018 2019 2020

Hazard Development

Expedited Interim

Evaluations

Risk Evaluations

Higher Priority

Lower Priority

CEUS

CEUS

Group 1

Only plants with new

seismic hazard exceeding

design basis

All plants

Hazard Analyses

WUS

Group 3 (as needed)

WUS

Group 2

Risk Evaluations

plant mods

plant mods

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● Staff Assessment or response

√ Staff acknowledgement to use GMRS for risk evaluation

Expedited Interim Evaluations

Schedule for Seismic Hazard and Risk Evaluations

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Forthcoming Seismic Screening Letter

• Issuance of letter for WUS sites in ~ 2 weeks• Diablo Canyon has screened-in for further

risk evaluations and is a review priority• No immediate safety issues identified• Information supports safety assurance

allowing additional time to complete the seismic risk evaluation

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List of Acronyms• CEUS – Central and Eastern United States• GMRS – Ground Motion Response Spectrum• NRC – U.S. Nuclear Regulatory Commission• NPP – Nuclear Power Plant• NTTF – Near‐Term Task Force• SFP – Spent Fuel Pool• SMA – Seismic Margins Analysis• SPID ‐ Screening, Prioritization, and Implementation Details SPID• SPRA – Seismic Probabilistic Risk Assessment• SSC – Structures, Systems and Components• SSHAC – Senior Seismic Hazard Analysis Committee • SSE – Safe Shutdown Earthquake• SPID – Screening, Prioritization, and Implementation  Details• WUS – Western United States 

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Break for NRC Staff Alignment

• 15 – 20 minute planned break for NRC staff alignment to support meeting wrap-up

• Meeting to resume at 4:00pm (Eastern) or 1:00pm (Western)

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Opportunity for Public Questions or Comments

• Additional Questions? Please ask us at:

JLD_PublicResource@nrc.gov

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Backup Slides

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Additional WUS Seismic Hazard

Reports

Public SSHAC Reports• Diablo Canyonhttp://www.pge.com/en/safety/systemworks/dcpp/sshac/index.page

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Guidance Documents

• Two main guidance documents proposed by industry and endorsed by the NRC

• Screening, Prioritization, and Implementation Details (SPID)– Submitted by EPRI on November 2012– Endorsed by NRC on February 15, 2013– EPRI-1025287 (ML12333A170)

• Seismic Evaluation Guidance: Augmented Approach (aka Expedited Approach)– Submitted by EPRI on April 9, 2013– Endorsed by NRC on May 7, 2013– EPRI-3002000704 (ML13102A142)

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Seismic 2.1 Process Ensures Clarity, Consistency, and Risk-Informed Regulatory Decisions

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NRC makes Regulatory Decisions as Needed

* Safety Enhancements* Backfit Analysis* Modify Plant License

PHASE 2DECISION-MAKING

Interact with Industry on Hazard and Risk

Evaluation Guidance

CEUS Licensees submit Site Response (9/2013 &

3/2014)

Licensees submit Hazard Reevaluations and

Interim Evaluations, as needed (3/2014, CEUS;

3/2015, WUS)

Screen and prioritize plants for Risk Evaluation.

Review Interim Evaluations, as needed

(CEUS:5/2014; WUS:5/2015)

Screened-in plants complete Expedited

Approach Interim(CEUS:12/31/2014;WUS:1/2016)

and Risk Evaluation(Group 1: 2017)

NRC reviews Risk Evaluation

PHASE 1

STAGE 1 STAGE 2INFORMATION GATHERING